Vine didn’t license music the way TikTok did IIRC. That gave TikTok a core use case tapping into kareoke-culture while Vine struggled to find a mainstream audience. Vine also had a slightly-shorter format with less creator tools, and altogether this meant the platform was much more constrained I think.

Also, from the outside at least, it felt like twitter just gave up with Vine (and periscope) after a single attempt at monetization. I suspect some of the other difference was the huge bankroll for user acquisition that TikTok had and the resulting patience around monetization? But I don’t know if that is true.